This invention relates to self-propelled institutional or commercial type lawn mowers, and is especially directed to large lawn mowers intended for extended service on a daily basis, e.g. by commercial landscape gardeners or ground maintenance personnel responsible for attending to lawns at corporate or government office parks, golf courses, condominiums, and the like. The invention is especially directed to walk-behind and sulky-type riding mowers in which there is an operator position situated behind the mowing mechanism.
At present, most lawn mowers of this type employ belt drives both for the mower blade and for the drive wheels. In these current mowers, each wheel is belt driven and is provided with a clutch and an individual wheel-brake which are intimately linked. The belts wear out quickly and the drive thus has a high maintenance rate. The belts also tend to slip when the grass is wet. Changing speeds requires disengaging both belts by squeezing hand calipers found on each handle bar. A speed selector control must then be adjusted to effect speed change. Because these actions take considerable time to accomplish, the operator usually opts not to make speed changes. This, however, renders precision mowing near obstacles difficult or impossible. Consequently, an intolerable amount of follow-up mowing with a hand mower or trimmer is usually required The operator must also release his grip on the steering controls when making various machine adjustments; this can and often does lead to an accident.
These same hand calipers when squeezed to their maximum positions engage a brake which is used for turning purposes. Because the hand calipers are spring controlled, they require considerable hand pressure to engage. This continuous hand pressure is extremely tiring. Due to the direct-drive, nondifferential type axle, almost continuous squeezing is required to keep the mower steered in the proper direction.
Previous walk-behind mowers generally do not have a reverse speed. Because of the excessive weight distribution, manual backing of the mower is extremely tiring on the operator and is often dangerous.
An improved mower that employs a hydrostatic transmission has been proposed in U.S. Pat. No. 4,787,195. That patent describes a self-propelled lawn mower that has a mowing deck that supports one or more blades. A pair of drive wheels are rotatably supported in a power deck located behind the mowing deck. Drive linkages convey power from an engine mounted upon the power deck to the rear drive wheels and also to a blade drive system for rotating the mowing blades An operator position is situated rearward of the drive wheels. The mower includes handle arrangement behind the drive wheels with operator controls mounted on the handle for selectively controlling the speed and direction of the drive wheels. In the mower of that patent, a hydrostatic transmission has an input shaft driven by the engine, and output shaft arranged to turn the drive wheels, and a control shaft that is rotated to control the ratio of the output shaft speed to the input shaft speed in a continuous range of speeds from reverse, through neutral, to maximum forward speed. The operator controls include a transmission control lever that is connected, for example, via a cable or a rigid linkage, to the control shaft of the hydrostatic transmission to enable the operator to select a desired drive wheel speed without removing his or her hand from the steering handle. The input shaft of the hydrostatic transmission can be vertically disposed, and the control shaft is either vertically or transversely disposed. A control lever for the hydrostatic transmission can be a C-shaped or L-shaped member that is connected at one end to the control shaft, with a control cable connected between the control handle and this member. A cooling fan can be mounted on the shaft of the hydrostatic transmission for air cooling the same. The drive wheels are connected to the hydrostatic transmission through a differential-type drive system whose differential right and left output shafts serve as axles on which the drive wheels are mounted. These output shafts are provided with independent right and left disk brakes, with separately actuated operating levers, so that the operator can brake the wheels independently for precision steering of the mower.
The engine is mounted with its center of gravity rearward of the drive wheel shaft, to serve as a counterweight or counterpoise to balance the weight of the mowing deck. Consequently, the mower center of gravity is disposed at or close to the drive wheel axle. This aids traction significantly and facilitates steering of the machine.
The small to medium size hydrostatic-drive mower can be steered in either of two ways:
1. Because of the differential drive, the operator can simply apply body weight to the handle bars to make directional changes. This is impossible with previous mowers because their wheels are not differentially coupled to the drive shaft.
2. Each wheel is fitted with a disk brake which is engaged by means of a hand lever on a correspondingly handle grip.
Engaging the disk brake is much easier than engaging the hand brake on other mowers because there is no spring-actuated clutch in the disk brake linkage.
Squeezing a selected hand caliper to engage one of the disk brakes results in an almost effortless turn toward the braked-wheel side of the machine.
These mowers can quickly turn one-hundred-eighty degrees to mow a row alongside a just-mowed row. To do this, the operator simply squeezes one brake lever, and releases the grip of the other hand. The differential drive then pulls the mower around and, and when turned, the operator simply releases the brake lever and resumes mowing.
Unfortunately, the effect of the differential drive is to transfer all of the power to the unbraked wheel at double the wheel speed that was experienced when both wheels were unbraked. This makes the mower rather difficult to control, unless the transmission control can be moved to a lower setting to keep the wheel speed even. However, in the arrangement of U.S. Pat. No. 4,787,195, the control lever is on one side of the handle bar, the operator can effect a hand brake turn only in one direction, i.e. only to the right where the control lever is mounted near the right hand grip.
An improved mower, controls are provided on both the right and left hand grips for controlling the speed of the hydrostatic transmission drive to the rear wheels, as described in U.S. Pat. No. 4,920,734. That mower has independent right and left disk brakes and a hydrostatic transmission which is driven by the mower's engine and an output that is connected through a differential drive to the right and left rear wheels. The control mechanism includes a pair of operating levers on the handle grips with a linkage connecting both operating levers to the speed regulator of the hydrostatic transmission. The operator can adjust the speed setting of the hydrostatic transmission using either hand without having to release his or her hands from the hand grips and without having to uncouple the transmission from the engine.
The control mechanism comprises a pair of thumb levers pivotally mounted on the handle bar assembly adjacent the respective hand grips. These are pushed forward to move the hydrostatic transmission to a forward speed, and are pulled back to move the hydrostatic transmission to a reverse speed. The two levers are each linked through a common linkage to the actuator of the transmission, so that the speed can be controlled with either lever. This permits effective one-hand braking and speed control so that the operator can carry out a high-speed hand-brake turn without relinquishing the control over wheel speed. This advantage comes about because the operator can reduce the operating wheel speed, by backing off the thumb lever slightly, to counter the effect of the differential, which would otherwise double the speed of the unbraked, outer wheel.
The control assembly linkage can include a pivot rod mounted transversely beneath the mowing deck with arms that are coupled through rigid connecting rods to the thumb levers. Another arm on this pivot rod is coupled through a connecting rod to the actuator levers for the hydrostatic transmission. Motion of either or both thumb lever will rotate the pivot rod and move the actuator lever. A spring return on the mower is connected to the actuator lever so that the actuator lever will seek neutral as soon as the thumb levers are released.
The thumb levers are somewhat spoon shaped, i.e., bent forward and then extending upward and are adjustably mounted on a rocker plate so that they can accommodate different hand sizes. This arrangement permits the operator to provide continuous pressure on the lever without significant fatigue. Also, for safety considerations, backing the mower requires pulling back on the lever or levers, and rearward motion stops as soon as the control levers are released.
A belt-loop-coil operator presence switch can be included to shut the mower down if the operator loses control of the mower.
This system works well for small to medium size commercial mowers (36 inches to 48 inches width). However, for larger mowers (e.g., 52 inches or wider) it is more convenient for the operator to control the speed to each drive wheel individually. In many locations, especially where the terrain is not level, more power has to be applied to one wheel or the other to keep the mower moving straight ahead. On a slope, the mower has a tendency to turn downhill. If the mower is of the larger type, the mower is often far too heavy for the operator simply to manhandle; braking the uphill side to control the direction is not precise, and also causes rapid wear of brake pads.
One extra-wide walk-behind mower has recently been proposed with a dual hydraulic drive system, in which the engine drives a pair of hydraulic pumps, each of which is connected to a hydraulic motor, one motor propelling the left drive wheel and the other motor propelling the right drive wheel. In this particular design, motion is controlled entirely by left and right squeeze levers that control the fluid flow between each of the hydraulic pumps and its respective motor. There are no brakes as such. The handles are squeezed to reverse the torque onto the drive wheels. Releasing the levers puts the mower in full forward. Also, this design mower does not default to a neutral condition, so if the operator loses control of the mower, the mower will continue to propel itself forward at full speed.
The industry has been seeking a reliable, safe extra-width walk-behind mower, with positive speed control to each drive wheel and fail-safe braking or stopping for each wheel, but such a mower has not been available.